I got one of the first 2014 899's in the USA and have been racing it since day one. I, like you, am a long time Ducati racer with my last Ducati racebike being a 1997 748 that was built to the max (rods, pistons, light crank, light wheels, fancy master cylinders etc). In between I did a short stint on a 2004 Aprilia Factory RSVR. I've also raced everything from SVs to 125 two strokes to the R6.
I can say, without question, that the 899 is the best motorcycle I've ever owned. In 5 seasons of racing I've had to adjust one exhaust valve (checked every year) and replace one wheel speed sensor (because I botched one up during a wheel swap). Other than that the other repairs have been "self induced".
My build was intended to remain eligible for super sport / super stock classes, so I've been using the stock wheels, brake rotors, master cylinders etc. The engine is completely stock, and I really like it that way.
The front suspension (BPF Showa) was initially tuned by my friend Dave at STM Suspension | Motorcycle Suspension Tuning in Northern Colorado. Specializing in WP Suspension.
and later we added cartridges from GP suspension. This was a big improvement and is worth doing.
The rear suspension is a TTX unit off of an 1199s that we removed the electronic guts from and replaced with regular clickers. Again, a significant improvement.
I used the air ducts that came with the bodywork I added - (Armour Bodies) and controls from Woodcraft. I'm very happy with all of those choices.
It has a Termignoni full system on it (because I got a deal on it) but in further research the head tubes on the 899 are adequate to the task and the slip on system makes exactly the same HP and torque, so you can save yourself some money there.
I did an auto blip - wicked cool and I think it completely eliminates the need for a slipper clutch. I've been racing mine this whole time without a slipper and I don't miss it at all. It's also considerably easier on clutch plates than any bike I've ever had with a slipper clutch.
I deleted the ABS system, running lines directly from the masters to the calipers
The only other "big" mod I've made was to replace the lower radiator with the Febur oil cooler set up. I race in Utah and Colorado where we have both high ambient temperatures and high altitude. Combine this with the belly pan arrangement reducing the airflow through the bike and mine was consistently running very hot. I made this change for longevity and reliability. Now on the hottest days the water temp will sometime exceed 200F on the cool down lap, where before it would push 250F. It's an expensive, but worthwhile modification.
Following this season I decided to give up on remaining super stock legal and bought a set of BST wheels for the bike. Sinjin isn't kidding, the stock wheels on the 899 are, literally, the heaviest I've ever felt come with a Sportbike. Just pushing the bike around with the light wheels on it is a revelation. I'm sure I'll run over the inside curb when I turn in the first time on this thing now - the wheels are 1/2 the weight of the stock ones. I'll report more once I've ridden it (probably April).
It's a fansastic bike, again the best I've ever owned. It doesn't have the same "feel" when leaned over as the trellis frame Ducatis (or even my Aprilia if I'm honest), but it more than makes up for that with the rest of the rider experience.
It's a blast to ride and I hope you enjoy yours as much as I've enjoyed mine!
Feel free to reach out to me if you have any questions you think I can answer.